The present invention relates to tools for the machining of materials by milling or drilling. More particularly, the invention provides an improved form for an end mill having a semi-spherical cutting end, or flat cutting end, or drill end, the center area of which is configured to better eject chips and thus to improve the surface finish of the metal work piece and tool life.
End mills and drills are widely used in milling and drilling operations due to their versatile range of application and due to the moderate first cost of the tool. End mills and drills are often of cylindrical shape, and are available up to about 80 mm diameter. End mills having a semispherical cutting end (referred to as ball end or ballnose) are widely used, being particularly useful for CNC work producing complex shapes. End mills with flat cutting end are widely used in ramping, planing, orbital drilling, and drilling applications. Drills are widely used in different drilling applications on milling and turning machines. An end mill typically has 2 to 10 teeth, depending on diameter size and whether the end mill is intended for rough cutting or finishing. End mills with a flat cutting end used in ramping, planing, orbital drilling, and drilling applications typically have 2 to 6 teeth. Drills used in different drilling applications on milling and turning machines typically have 2 to 4 teeth. Teeth are usually of spiral (helical) shape, but can be straight parallel to the axis. Some materials used in the construction of such mills and drills include high speed steel, solid carbide, cermet or ceramic, or combinations thereof.
An important problem which has attracted much attention is the clearing away of the chips produced during machining. Milled and drilling chips are never continuous, and, if not removed, may again be drawn into the cutting area between one of the cutting teeth and the work piece. Similarly, the clearing away of the chips produced during machining is very important in drilling applications. The result of the not clearing away of the chips produced during machining is a degraded surface finish marred by small grooves or scratches, vibration during machining, short tool life and poor dimensional accuracy. While much can be achieved by improved coolant flow and by air blasts, an important further factor in effecting improvement is the shape of the cutting teeth.
Many different cutter forms are seen in the prior art. Among relevant patents are the following: Japanese application 2001047671 of Takeshi, Japanese patents JP2001334405 and JP2001009524 to Masami, JP2003053617 to Takeshi, JP2001341026 to Ryosuke, U.S. Pat. No. 4,934,881 to Tsujimura et al., U.S. Pat. No. 5,188,487 to Okawa et al., U.S. Pat. No. 5,221,162 to Okawa, U.S. Pat. No. 5,294,219 to Shiratori et al., and U.S. Pat. Nos. 6,231,275 B1 and 6,652,201 B2 to Kunimori et al.
Cutters made according to the Japanese patents JP2001334405 and JP2001341026 have been found to provide inadequate chip clearance causing chip reentry and also insufficient access for coolant to the center of the end mill.
Unfortunately, without carefully controlled test machining, there is no way of knowing how effective the prior art end mill forms are merely from the description of the tooth geometry provided. Furthermore, the tooth designs disclosed in the above documents may be optimized for maximum metal removal, or for maximum tool wear life or for resistance to breakage, or for hard or for soft materials, and the tooth form will vary greatly as a function of the different design parameters, and of the cutter diameter.
Extensive experience with various prior-art cutters has however indicated the continued existence of surface flaws in work pieces machined by prior art ballnose end mills, and the root of the problem has been traced to chips which were not dispersed by the coolant. These chips reentered the cutting area and, in the course of machining, lodged momentarily between the end mill and the work piece.